Implantable system and method for measuring left atrial pressure to detect, diagnose and treating congestive heart failure

ABSTRACT

The invention provides improved apparatus and methods for treating congestive heart failure in a medical patient. The apparatus includes a pressure transducer permanently implantable within the left atrium of the patient&#39;s heart and operable to generate electrical signals indicative of fluid pressures within the patient&#39;s left atrium. The pressure transducer is connected to a flexible electrical lead, which is connected in turn to electrical circuitry, which in the preferred embodiment includes digital circuitry for processing electrical signals. The electrical circuitry processes the electrical signals from the pressure transducer and, based at least in part on those signals, generates a signal that indicates a desired therapeutic treatment for treating the patient&#39;s condition. That signal is then communicated to the patient via a patient signaling device, following which the patient administers to him or herself the prescribed therapeutic treatment indicated by the signal.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/127,227 filed on Apr. 19, 2002, which is a continuation of U.S.application Ser. No. 09/956,596, filed on Sep. 19, 2001, now abandoned,which is a continuation of U.S. application Ser. No. 09/481,084, filedon Jan. 11, 2000, now issued as U.S. Pat. No. 6,328,699, all hereinincorporated by reference.

BACKGROUND OF THE INVENTION

Heart failure is a condition in which a patient's heart works lessefficiently than it should, a condition in which the heart fails tosupply the body sufficiently with the oxygen rich blood it requires,either at exercise or at rest. Congestive heart failure (CHF) is heartfailure accompanied by a build-up of fluid pressure in the pulmonaryblood vessels that drain the lungs. Transudation of fluid from thepulmonary veins into the pulmonary interstitial spaces, and eventuallyinto the alveolar air spaces, is called pulmonary edema, and can causeshortness of breath, hypoxemia, acidosis, respiratory arrest, and death.

It is estimated that about four million people in the United Statessuffer from various degrees of heart failure. Although CHF is a chroniccondition, the disease often requires acute hospital care. Patients arecommonly admitted for acute pulmonary congestion accompanied by seriousor severe shortness of breath. Acute care for congestive heart failureaccounts for the use of more hospital days than any other cardiacdiagnosis, and consumes in excess of seven and one-half billion dollarsin the United States annually.

It is far more cost effective, and much better for the patient's health,if chronic CHF can be managed and controlled by the routineadministration of appropriate drug therapy rather than by hospitaltreatment upon the manifestation of acute symptoms. Patients withchromic CHF are typically placed on triple or quadruple drug therapy tomanage the disease. The drug regimen commonly includes diuretics,vasodilators such as ACE inhibitors or A2 receptor inhibitors, andinotropic agents usually in the form of cardiac glycosides such asDigoxin. Patients may also be placed on beta blockers such asCarvedilol.

As with all drugs, these agents must be taken in doses sufficient toensure their effectiveness. Problematically, however, over-treatment canlead to hypotension, renal impairment, hyponatremia, hypokalemia,worsening CHF, impaired mental functioning, and other adverseconditions. Adding to the challenge of maintaining proper drug dosage isthe fact that the optimal dosage will depend on diet, particularly saltand fluid intake, level of exertion, and other variable factors. Addingfurther to the problem of managing this condition is the fact thatpatients frequently miss scheduled doses by forgetting to take pills ontime, running out of medications, or deciding to stop medicationswithout consulting their physician. It is important, therefore, that thepatient's condition be monitored regularly and thoroughly, so thatoptimal or near optimal drug therapy can be maintained. This monitoringis itself problematic, however, in that it requires frequent visits witha caregiver, resulting in considerable inconvenience and expense.

It would be highly advantageous, therefore, if methods and apparatuscould be devised by which a patient's congestive heart failure could bemonitored routinely or continuously with minimal attendance by acaregiver, and then only when actually required. It would be furtheradvantageous if such methods and apparatus included means forcommunicating diagnostic information not only to the physician but tothe patient himself, so that the patient could continue or modify hisown drug therapy appropriately and generally without the directintervention of a physician. The present invention provides these veryadvantages, along with others that will be further understood andappreciated by reference to the written disclosure, figures, and claimsincluded in this document.

SUMMARY OF THE INVENTION

The invention provides improved apparatus and methods for treatingcongestive heart failure in a medical patient. The apparatus includes apressure transducer permanently implantable within the left atrium ofthe patient's heart and operable to generate signals indicative of fluidpressures within the patient's left atrium. The pressure transducer isconnected in turn to signal processing apparatus, which in the preferredembodiment includes digital circuitry for processing electrical signals.The signal processing apparatus processes the electrical signals fromthe pressure transducer and, based at least in part on those signals,generates a signal that indicates a desired therapeutic treatment fortreating the patient's condition. That signal is then communicated tothe patient via a patient signaling device, following which the patientadministers to him or herself the prescribed therapeutic treatmentindicated by the signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and operation of the invention will be better understoodwith the following detailed description of preferred embodiments of theinvention, along with the accompanying illustrations, in which:

FIG. 1 depicts apparatus suitable for practicing the invention;

FIG. 2 is a schematic sectional view of a patient's heart showing a partof the apparatus of the invention positioned therein;

FIG. 3 depicts a method for anchoring within the patient's heart aflexible electrical lead that comprises a part of the apparatus forpracticing the invention;

FIG. 4 shows an alternative method for anchoring a lead within theheart, including a helical screw for advancement into the patient'satrial septum;

FIG. 5 shows the apparatus depicted in FIG. 4, with a pressure sensingtransducer in place in the patient's left atrium;

FIG. 6 depicts a flexible lead including deployable anchors carriedinside a removable sheath and placed through the atrial septum;

FIG. 7 shows the flexible lead of FIG. 6 with the sheath withdrawn todeploy the anchors on opposite sides of the atrial septum;

FIG. 8 shows the flexible lead of FIGS. 6 and 7, with a pressure sensingtransducer in place inside the patient's left atrium; and

FIG. 9 is a schematic diagram depicting digital circuitry suitable foruse in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a system for continuously or routinely monitoringthe condition of a patient suffering from chronic congestive heartfailure (CHF). As will be described in detail below, a systemincorporating the invention monitors the patient's left atrial pressure,and, depending upon the magnitude of or changes in this pressure, thesystem communicates a signal to the patient indicative of a particularcourse of therapy appropriate to manage or correct, as much as possible,the patient's chronic condition.

Elevated pressure within the left atrium of the heart is the precursorof fluid accumulation in the lungs which is symptomatic of acute CHF.Mean left atrial pressure in healthy individuals is normally less thanabout twelve millimeters of mercury (mm Hg). Patients with CHF that havebeen medically treated and clinically “well compensated” may generallyhave mean left atrial pressures in the range from fifteen to twenty mmHg. Transudation of fluid into the pulmonary interstitial spaces can beexpected to occur when the left atrial pressure is above abouttwenty-five mm Hg, or at somewhat more than about thirty mm Hg in somepatients with chronic CHF. Pulmonary edema has been found to be veryreliably predicted by reference to left atrial pressures, and much lesswell correlated with conditions in any other chamber of the heart. Thus,the methods and apparatus of the invention are expected to prove veryuseful in treating and preventing pulmonary edema and other adverseconditions associated with CHF.

A system according to the invention includes a pressure sensor that isimplanted within the patient and positioned to measure pressures withinthe patient's left atrium. Signals from the pressure sensor aremonitored continuously or at appropriate intervals. Physician-programmedcoded communications are then transmitted to the patient correspondingto appropriate drug therapies that the patient may in most casesadminister to him or herself without further diagnostic interventionfrom a physician.

Apparatus 5 for practicing the invention is depicted in FIG. 1. Theapparatus comprises a housing 7 and a flexible, electrically conductivelead 10. The lead is electrically connectable to the housing through aconnector 12 on the exterior of the housing. The housing is outwardlysimilar to the housing of an implantable electronic defibrillatorsystem. Defibrillator and pacemaker systems are implanted routinely inmedical patients for the detection and control of tachy- andbradyarrythmias.

The flexible lead 10 is also generally similar to leads used indefibrillator and pacemaker systems, except that a compact pressuretransducer 15 is disposed at the distal end 17 of the lead, opposite theconnector 12 on the housing 7. The pressure transducer measures fluidpressure in its immediate vicinity. An electrical signal or another formof signal indicative of this pressure is then transmitted along the leadthrough the connector and from there to circuitry inside the housing.

The left atrium can be accessed from the right atrium through the atrialseptum separating the right and left atria. The flexible lead 10 andpressure transducer 15 will be anchored to the atrial septum. Thisplacement can be achieved using vascular access techniques that arewell-known to those familiar with the performance of invasivecardiovascular procedures, and in particular to interventionalcardiologists and cardiovascular surgeons. These procedures are commonlyperformed with the aid of visualization techniques including standardfluoroscopy, cardiac ultrasound, or other appropriate visualizationtechniques used alone or in combination.

Access to the central venous circulation may be achieved by use of thestandard Seldinger technique through the left or right subclavian vein,the right or left internal jugular vein, or the right or left cephalicvein. Alternatively, access may be made via the Seldinger technique intothe right femoral vein. In either case, a Brockenbrough catheter andneedle are used to pierce the atrial septum for access to the leftatrium.

FIG. 2 provides a schematic sectional view of the patient's heart andshows the apparatus used to access the left atrium. FIG. 2 depicts anaccess assembly 18 comprising a Brockenbrough catheter 20 inside apeel-away sheath 22, with a flexible guidewire 25 residing within theBrockenbrough catheter. As FIG. 2 indicates, the access assembly hasbeen placed through the superior vena cava 28 into the right atrium 30of the heart 33. FIG. 2 shows as well the inferior vena cava 35, theleft atrium 36, the right ventricle 37, the left ventricle 40, theatrial septum 41 that divides the two atria, and the valves 42 betweenthe right atrium and right ventricle, and the left atrium and leftventricle. The reader will appreciate that the view of FIG. 2 issimplified and somewhat schematic, but that nevertheless FIG. 2 and theother views included herein will suffice to illustrate adequately theplacement and operation of the present invention.

With the access assembly 18 in place within the right atrium 30, theBrockenbrough catheter 20 is used to pierce the atrial septum 41 byextending the Brockenbrough needle (not shown) through the atrial septuminto the left atrium 36. In the figures, the atrial septum has beenpierced by the needle, the catheter 20 advanced over the needle, and theneedle withdrawn from the catheter leaving the catheter in place insidethe left atrium. Optionally, a guidewire may be advanced through theneedle into the left atrium before or after advancing the catheter, orit may be placed into the left atrium through the catheter alone afterthe needle has been withdrawn.

As indicated by the arrows 45 in FIG. 2, the peel-away sheath 22 mayextend into the left atrium, or it may remain on the near side of theatrial septum within the right atrium 30. FIG. 2 shows the guidewire 25extended from the end of the Brockenbrough catheter to secure continuousaccess into the left atrium. As depicted therein, the guidewire has acurled, “pig-tail” style distal tip 48 to better secure the guidewirewithin the left atrium and to safeguard against inadvertent withdrawalthrough the atrial septum. Once the guidewire is in place in the leftatrium, the Brockenbrough catheter is withdrawn so that the flexiblelead 10 (see FIG. 3) may be placed through the peel-away sheath 22.

The reader may appreciate that the configuration shown in FIG. 2 is onethat results from an approach from the superior venous circulationthrough the superior vena cava. If the approach is made from theinferior venous circulation through an entry into the right femoralvein, access into the right atrium 30 will be made via the inferior venacava 35.

If the approach is made from the inferior venous circulation, anadditional procedure is required to transfer the proximal end of theguidewire to the superior venous circulation after its distal end hasbeen placed into the left atrium. This must be done to allow the sensorand its lead to be inserted over the guidewire from a superior vein intothe left atrium. One method for transferring the proximal end of theguidewire from an inferior to a superior vein is to use a guidewire thathas a preformed bend somewhere along its central body. After the atrialseptum 41 is penetrated and the distal tip of the guidewire placed inthe left atrium 36, the Brockenbrough catheter and sheath are withdrawnto a point just proximal of the guidewire bend. Then, with care beingused to maintain the distal tip of the guidewire in place in the leftatrium, the needle and sheath are used to push the central body of theguidewire into the superior venous circulation. A guidewire hook (notshown) may then be used to retrieve the guidewire body through an accesssheath placed into the superior venous system so that the proximal endof the guidewire extends out of the patient through the patient'ssuperior venous circulation.

Either approach described above results in the placement of a guidewirewith its distal tip in the left atrium 36 and extending (in the proximaldirection) through the atrial septum 41, the right atrium 30, thesuperior vena cava 28, and out of the patient's body through a superiorvenous access site. These approaches are generally conventional andwidely known in the medical arts. While neither is a trivial procedure,they are both well within the capabilities of a skilled interventionalcardiologist, radiologist, vascular or cardiac surgeon, or a similarlyskilled medical practitioner.

With the guidewire 25 securely in place with its distal tip 48 insidethe left atrium 36, the flexible lead 10 may be advanced into the leftatrium. The flexible lead might itself include a central lumenconfigured to receive the proximal end of the guidewire, therebyallowing the flexible lead to be advanced down the guidewire toward theleft atrium. More commonly, an exchange catheter, which may be in theform of a peel-away sheath 22, will be advanced down the guidewire andplaced into the left atrium, after which the flexible lead will beadvanced down the exchange catheter and into position. Once the pressuretransducer of the flexible lead is positioned within the left atrium,the lead should be anchored in place to ensure that the pressuretransducer stays reliably and permanently in the desired location.

One method for anchoring the flexible lead 10 in place is depicted inFIG. 3, which is like FIG. 2 a somewhat schematic depiction of some ofthe major structures of the heart. FIG. 3 shows the four pulmonary veins50 that connect to the left atrium 36. In the particular apparatusdepicted in FIG. 3, the flexible lead 10 includes a pressure transducer15 located on the body of the lead a short distance proximal of thedistal end 17 of the lead.

As FIG. 3 indicates, the distal end 17 of the flexible lead 10 in thisembodiment can be bent by the operator in much the same way as a distaltip such as might be found on a steerable angioplasty guidewire oranother similar device. This feature assists the operator in steeringthe flexible lead into a selected one of the pulmonary veins 50, withthe pressure transducer 15 disposed within the interior space of theleft atrium 36, or even within the pulmonary vein itself. Placement ofthe pressure transducer within the pulmonary vein is effective becausepressures within the pulmonary vein are very close to pressures withinthe left atrium. It will be appreciated by those skilled in the art thatvisualization markers (not shown) may be provided at appropriatelocations on the flexible lead to assist the operator in placing thedevice as desired. With the flexible lead in place as shown, the body'sOwn natural healing mechanism will permanently anchor the flexible leadin place both at the penetration site through the atrial septum 41, andwhere the flexible lead contacts the interior surface of the pulmonaryvein in which the tip of the lead resides. The pressure transducer mightalso be placed at locations such as the left atrial appendage or theleft ventricular cavity, regions in which pressures are nearly the sameas pressures in the left atrium.

FIGS. 4 and 5 show alternative means for anchoring the pressuretransducer in a location appropriate for measuring pressures within theleft atrium 36. The lead in this embodiment includes a helical screwthread for anchoring the lead to the atrial septum 41. Similarconfigurations are used in some leads for pacemakers and thus may befamiliar to those skilled in the art.

Referring now specifically to FIG. 4, the guidewire 25 is shownpositioned across the atrial septum 41 between the left atrium 36 andthe right atrium 30. A first lead component 53 is delivered over theguidewire through an appropriate guiding catheter 55 or sheath. Thisfirst lead component includes a helical screw 57 on its exteriorsurface. The helical screw is advanced into the tissue of the atrialseptum by applying torque to the shaft of the first lead component. Thehelical screw could also be coupled to a hollow or solid cylindricalmandrel (not shown), or to a spirally wound mandrel (also not shown)disposed along substantially the entire length of the first leadcomponent. When the helical screw has been turned and advancedsufficiently into the atrial septum, the guidewire and guiding cathetermay then be withdrawn leaving the first lead component anchored securelyin place.

With the guidewire having been removed, a second lead component 60 isadvanced as shown in FIG. 5 through the central lumen of the first leadcomponent 53. The first and second lead components are sized andconfigured so that when the second lead component is fully advanced withrespect to the first lead component, a left atrial pressure transducer62 at the end of the second lead component protrudes by an appropriatepredetermined amount into the left atrium 36. The second lead componentis then securely fixed with respect to the first lead component.

It should be noted that the embodiment depicted in FIGS. 4 and 5includes a second pressure transducer 65 on the exterior of the firstlead component 53 and exposed to pressure within the right atrium 30.This illustrates in a simplified way a general principle of theinvention, in which a pressure transducer is used to measure fluidpressure within the left atrium, but in which one or more additionaltransducers or sensors may also be used to detect a physiologiccondition other than left atrial pressure. These physiologic conditionsmay include pressures in locations other than the left atrium 36, andphysical parameters other than pressure, either within the left atriumor at other locations.

FIGS. 6, 7, and 8 show another embodiment of a flexible lead 10 suitablefor use with the invention, in which folding spring-like fins or anchorsdeploy to anchor the lead in place in the atrial septum 41. Referringspecifically to FIG. 6, a first lead component 53 is advanced through asheath 67, the sheath having been advanced across the atrial septum. Inthis embodiment, the first lead component includes folding distalanchors 68 and proximal anchors 70, which lie folded and are held inplace inside the interior lumen of the sheath. When the first leadcomponent and sheath are properly positioned, which will generallyinvolve the use of fluoroscopy or an alternative technique for imaging,the operator may carefully withdraw the sheath from around the firstlead component. As the distal and proximal anchors exit the sheath, theydeploy themselves (as depicted in FIG. 7) on either side of the atrialseptum, thereby anchoring the first lead component securely in place.Similar anchors are sometimes used with leads for pacemakers and othermedical devices where permanent anchoring is desired, and the operationof these anchors will thus be not entirely unfamiliar to theknowledgeable reader.

Referring now to FIG. 8, a second lead component 60 is advanced througha central lumen of the first lead component 53 after the guidewire 25(see FIGS. 6 and 7) and sheath 67 are removed. As in the previousembodiment, a left atrial pressure transducer 62 is carried at thedistal end of the second lead component. Again, the first and secondlead components are sized and configured with respect to one another sothat the left atrial pressure transducer protrudes from the first leadcomponent an appropriate amount into the left atrium 36. Also as in theprevious embodiment, a second pressure transducer 65 on the exterior ofthe first lead component allows for the measurement and transmittal ofpressure within the right atrium 37.

Alternative systems and methods have been described for anchoring aflexible lead with a pressure transducer disposed to measure pressurewithin the patient's left atrium. Other anchoring methods may be devisedby those skilled in the relevant arts without departing in any way fromthe principles of the invention. Moreover, approaches have beendescribed by which the lead is positioned between the left atrium and anexit site from the patient's superior venous circulation. Alternate leadroutes and exit sites may find use as well.

Referring back to FIG. 1, an exit from the superior venous system isadvantageous because, with the flexible lead 10 connected to the housing7 via the connector 12, the housing may be surgically implanted into thepatient's body, typically in a subcutaneous pocket, which may be formed,e.g., in the shoulder area in proximity to the patient's clavicle, in amanner quite similar to that routinely performed to implant pacemakersand implantable cardiac defibrillators. The device described herein maythus be implanted and operational within the patient's body for extendedperiods.

Coaxial lead configurations as described, in which a central leadportion carrying a sensor is inserted in an outer lead portion carryinganchoring apparatus after the anchoring apparatus is deployed, areadvantageous for a number of reasons. First, the lead portion carryingthe anchoring apparatus is advanced to the target site over a guidewire,which remains in place until the anchoring apparatus is securelydeployed. If difficulty is encountered in deploying the anchoringapparatus, the outer lead portion may be repositioned or even replacedwith a different outer lead portion, without removing the guidewire fromits position. Secure access to the target site may thereby be maintainedthroughout the procedure.

This configuration has a further advantage in that the second, innerlead component may be conveniently replaced through the first, outerlead component in the event that the second lead component fails.Moreover, the inner lead component carrying the sensor may even bereplaced, even at a much later time, if, for example, a new and moreadvanced sensor becomes available through further development.

As will be described in more detail below, the system includes circuitryand signaling means that will require power from a compact batterylocated inside the housing. Those skilled in the art will appreciatethat the device may thus require periodic explantation so the batterymay be refreshed, or more usually so that the entire unit comprising thehousing, the battery, and the internal circuitry can be replaced with anew unit. Nevertheless, it should be possible to leave the device inplace inside the patient's body for extended periods comparable to thoseexperienced in connection with pacemakers and implantabledefibrillators, and implantation for such extended periods is describedin this document as being substantially “permanent.”

The function and operation of the apparatus housed inside the housingwill now be described. FIG. 9 is a schematic diagram of operationalcircuitry located inside the housing 7 and suitable for use with theinvention. The apparatus depicted in FIG. 9 includes digital processors,but the same concept could also be implemented with analog circuitry.

As described above, the system of the invention includes a pressuretransducer 73 permanently implanted to monitor fluid pressure within theleft atrium of the patient's heart. The system may, moreover, includeone or more additional sensors 75 configured to monitor pressure at alocation outside the left atrium, or a different physical parameterinside the left atrium or elsewhere. For each sensor, a sensor lead 77and 80 conveys signals from the sensor to a monitoring unit 82 disposedinside the housing of the unit. It should also be noted that the sensorlead connecting the pressure transducer to the monitoring apparatusmight also be combined with or run parallel to another lead such as anelectrical EKG sensor lead or a cardiac pacing lead, either of whichmight be placed in or near the left atrium.

When the signal from the left atrial pressure transducer 73 enters themonitoring unit 82, the signal is first passed through a low-pass filter85 to smooth the signal and reduce noise. The signal is then transmittedto an analog-to-digital converter 88, which transforms the signals intoa stream of digital data values, which are in turn stored in digitalmemory 90. From the memory, the data values are transmitted to a databus 92, along which they are transmitted to other components of thecircuitry to be processed and archived. An additional filter 95,analog-to-digital converter 97, and digital memory area 100 may beprovided as shown for each optional sensor 75 whenever such a sensor ispresent.

From the data bus 92, the digital data are stored in a non-volatile dataarchive memory area 103. This archive stores the data for laterretrieval, for example, by a physician at the patient's next regularlyscheduled office visit. The data may be retrieved, for example, bytranscutaneous telemetry through a transceiver 105 incorporated into theunit. The same transceiver may serve as a route for transmission ofsignals into the unit, for example, for reprogramming the unit withoutexplanting it from the patient. The physician may thereby develop,adjust, or refine operation of the unit, for example, as new therapiesare developed or depending on the history and condition of anyindividual patient. Means for transcutaneous signal transmission areknown in the art in connection with pacemakers and implantable cardiacdefibrillators, and the transceiver used in the present invention may begenerally similar to such known apparatus.

The digital data indicative of the pressure detected in the left atrium,as well as data corresponding to the other conditions detected by othersensors, where such are included, are transferred via the data bus 92into a central processing unit 107, which processes the data based inpart on algorithms and other data stored in non-volatile program memory110. The central processing unit then, based on the data and the resultsof the processing, sends an appropriate command to a patient signalingdevice 113, which sends a signal understandable by the patient and basedupon which the patient may take appropriate action such as maintainingor changing the patient's drug regimen or contacting his or herphysician.

The patient signaling device 113 may be a mechanical vibrator housedinside the housing of the system, a device for delivering a small,harmless, but readily noticeable electrical shock to the patient, or insome embodiments, a low power transmitter configured to transmitinformation transcutaneously to a remote receiver, which would include adisplay screen or other means for communicating instructions to thepatient. The system may also include apparatus, e.g., cellular orland-line telephone equipment or a device connected to the Internet, forcommunicating information back to a base location. This could be used,for example, to transmit information concerning the patient's conditionback to a hospital or doctor's office, or to transmit informationconcerning the patient's prescription usage back to a pharmacy.

The circuitry of the invention may also include a power managementmodule 115 configured to power down certain components of the system,e.g., the analog-to-digital converters 88 and 97, digital memories 90and 100, and the central processing unit 107, between times when thosecomponents are in use. This helps to conserve battery power and therebyextend the useful life of the device so that it can remain operationalinside the patient's body for extended periods between maintenance orreplacement. Other circuitry and signaling modes may be devised by oneskilled in the art.

Exemplary modes of operation for the system of the invention will now bedescribed. The system may be programmed, for example, to power up onceper hour to measure the left atrial pressure and other conditions asdictated by the configuration of the particular system and any othersensors that might be present. Left atrial pressure measurements aretaken at a twenty hertz sampling rate for sixty seconds, yielding 1200data values reflective of the fluid pressure within the left atrium. Thecentral processing unit then computes the mean left atrial pressurebased on the stored values. Then, if the mean pressure is above athreshold value predetermined by the patient's physician, the centralprocessing unit causes an appropriate communication to be sent to thepatient via the patient signaling device.

A set of coded communications to the patient can be devised by thetreating physician and encoded into the device either at the time ofimplantation or after implantation by transcutaneous programing usingdata transmission into the non-volatile program memory 110 via thetransceiver 105. For example, assume that the physician has determinedthat a particular patient's mean left atrial pressure can be controlledat between 15 and 20 mm Hg under optimal drug therapy. This optimal drugtherapy might have been found to comprise a drug regimen including 5milligrams (mg) of Lisinopril, 40 mg of Lasix, 20 milliequivalents (mEq)of potassium chloride, 0.25 mg of Digoxin, and 25 milligrams ofCarvedilol, all taken once per twenty-four hour day.

The patient is implanted with the device and the device is programmed asfollows. Assume that the device includes a single pressure transducer 73(see FIG. 9) implanted across the atrial septum inside the patient'sleft atrium, that the device's programming provides for four possible“alert levels” that are specified according to mean left atrialpressures detected by the transducer and computed in the centralprocessing unit 107, and that the patient signaling device 113 is amechanical vibrator capable of producing pulsed vibrations readilydiscernable by the patient.

At predetermined intervals, perhaps hourly, the device measures thepatient's mean left arterial pressure as described above, and determinesthe appropriate alert level for communication to the patient accordingto programming specified by the physician. For example, a mean leftatrial pressure of less than 15 mm Hg could be indicative of some degreeof over-medication and would correspond to alert level one. A pressurebetween 15 and 20 mm Hg would indicate optimal therapy and correspond toalert level two. A pressure between 20 and 30 mm Hg would indicate mildunder-treatment or mild worsening in the patient's condition, and wouldcorrespond to alert level three. Finally, a mean left atrial pressureabove 30 mm Hg would indicate a severe worsening in the patient'scondition, and would correspond to alert level four.

When the proper alert level is determined, the device sends a two-secondvibration pulse to notify the patient that the device is about tocommunicate an alert level through a sequence of further vibrations. Afew seconds later, a sequence of one to four relatively short (onesecond) vibratory pulses, the number corresponding to the applicablealert level, are made by the device and felt by the patient. The patientcan easily count the pulses to determine the alert level, then continueor modify his own therapy with reference to a chart or otherinstructions prepared for him by the physician.

For example, two pulses would correspond to alert level two, an optimalor near optimal condition for that particular patient. In that case, thedoctor's instructions would tell the patient to continue his or hertherapy exactly as before. The signal for alert level two would be givenonce every 24 hours, at a fixed time each day. This would serve mainlyto reassure the patient that the device is working and all is well withhis therapy, and to encourage the patient to keep taking the medicationon a regular schedule.

One pulse, in contrast, would correspond to alert level one, and mostlikely some degree of recent over-medication. The doctor's orders wouldthen notify the patient to reduce or omit certain parts of his therapyuntil the return of alert level two. For example, the doctor'sinstructions might tell the patient temporarily to stop taking Lasix,and to halve the dosage of Lisinopril to 2.5 mg per day. The codedsignal would be given to the patient once every twelve hours until thereturn of the alert level two condition.

Three pulses would indicate alert level three, a condition of mildworsening in the patient's condition. Accordingly, the doctor'sinstructions would notify the patient to increase the diureticcomponents of his therapy until alert level two returned. For example,the patient might be instructed to add to his to his normal doses anadditional 80 mg of Lasix, twice daily, and 30 mEq of potassiumchloride, also twice daily. The level three alert signal would be givenevery four hours until the patient's condition returned to alert leveltwo.

Four pulses would indicate alert level four, indicating a seriousdeterioration in the patient's condition. In this case, the patientwould be instructed contact his physician and to increase his doses ofdiuretics, add a venodilator, and discontinue the beta-blocker. Forexample, the patient might be instructed to add to his therapy anadditional 80 mg of Lasix, twice daily, an additional 30 mEq ofpotassium chloride, twice daily, 60 mg of Imdur, twice daily, and tostop taking the beta-blocker, Carvedilol. The signal corresponding toalert level four would be given every two hours, or until the physicianwas able to intervene directly.

Apparatus as described herein may also be useful in helping patientscomply with their medication schedule. In that case, the patientsignaling device would be programed to signal the patient each time thepatient is to take medication, e.g., four times daily. This might bedone via an audio or vibratory signal as described above. In versions ofthe apparatus where the patient signaling device includes apparatus fortransmitting messages to a hand held device, tabletop display, oranother remote device, written or visual instructions could be provided.Apparatus could also be devised to generate spoken instructions, forexample, synthesized speech or the actual recorded voice of thephysician, to instruct the patient regarding exactly what medication isto be taken and when.

Where the system includes apparatus for communicating information backto a base location, e.g., the hospital, doctor's office, or a pharmacy,the system could be readily adapted to track the doses remaining in eachprescription and to reorder automatically as the remaining supply of anyparticular drug becomes low.

Advanced embodiments and further refinements of the invention mayincorporate sensors in addition to the left atrial pressure sensor. Thisgives rise to the possibility of further refined diagnostic modescapable of distinguishing between different potential causes ofworsening CHF, and then of signaling an appropriate therapeutictreatment depending upon the particular cause for any particularoccurrence.

For example, increased left atrial pressure is commonly caused byimproper administration of medication, patient non-compliance, ordietary indiscretion, e.g., salt binging. These causes will be generallywell-handled by changes in the patient's drug regimen like thosedescribed above.

There are other causes of increased left atrial pressures that are lesscommon, but by no means rare, and which require different therapies foradequate treatment. For example, one such potential cause is cardiacarrhythmia, and especially atrial fibrillation with a rapid ventricularresponse. Other arrythmias may contribute as well to worsening heartfailure. A system including an ECG electrode in addition to the leftatrial pressure sensor would allow the system to diagnose arrythmias anddetermine whether the arrhythmia preceded or came after the increase inleft atrial pressure. Depending on the unit's programming, as specifiedby the patient's physician, specific therapies could be signaledtailored to treat the specific causes and conditions associated withparticular adverse events.

Although the pressure transducer in the preferred embodiment produces anelectrical signal indicative of pressures in its vicinity and,accordingly, an electrical lead is used to transmit the signals to theelectronic circuitry, other types of pressure transducers may find useas well. For example, the pressure transducer and lead might comprise atube filled with an incompressible fluid leading from the left atriumback to a transducer in the housing or at another location. Signals inthe form of pressures in the incompressible fluid would then indicatepressures in the left atrium and those pressures would in turn be sensedby the transducer and utilized by the electronic circuitry in generatingsignals indicative of appropriate therapeutic treatments. Signals inother forms may be used as well and may be transmitted, for example, byfiber optic means, or by any other suitable electrical,electro-mechanical, mechanical, chemical, or other mode of signaltransmission.

Moreover, although the signal lead in the preferred embodiment is of anappropriate length so that the housing containing the electroniccircuitry can be implanted in the region of the patient's shoulder, thelead may in alternative embodiments be of virtually any useful length,including zero. It may be that an integrated unit might be used in whichthe pressure transducer is disposed directly on the housing and theentire device implanted inside or very near to the left atrium of thepatient's heart.

Certain presently preferred embodiments of apparatus and methods forpracticing the invention have been described herein in some detail andsome potential modifications and additions have been suggested. Othermodifications, improvements and additions not described in this documentmay also be made without departing from the principles of the invention.Therefore, the full scope of the invention must be ascertained byreference to the appended claims, along with the full scope ofequivalents to which those claims are legally entitled.

1. A method for treating congestive heart failure in a medical patient,the method comprising: implanting a cardiac pacing lead combined with asensor lead connected to a pressure transducer substantially permanentlywithin the medical patient; operating the pressure transducer togenerate a signal indicative of fluid pressure within the left atrium;communicating the signal indicative of the fluid pressure within theleft atrium to a signal processing apparatus; operating the signalprocessing apparatus to generate an instructive signal indicative of anappropriate therapeutic treatment, wherein operating the signalprocessing apparatus comprises generating one of at least two distinctsignals, each said signal indicative of a different therapeutictreatment; and communicating the instructive signal indicative of theappropriate therapeutic treatment to the patient.
 2. The method of claim1, and further comprising implanting at least a portion of the signalprocessing apparatus substantially permanently within the patient'sbody.
 3. The method of claim 1, and further comprising anchoring thepressure transducer to the patient's atrial septum.
 4. The method ofclaim 3, wherein implanting the signal processing apparatus within thepatient's body comprises implanting the signal processing apparatus in asubcutaneous pocket in the region of the patient's shoulder.
 5. Themethod of claim 3, wherein anchoring the pressure transducer to thepatient's atrial septum comprises advancing a helical screw into thepatient's atrial septum.
 6. The method of claim 3, wherein anchoring thepressure transducer to the patient's atrial septum comprises deployingat least one anchor by spring force to bear against the patient's atrialseptum.
 7. The method of claim 1, wherein communicating the signalindicative of the appropriate therapeutic treatment comprises generatingan electrical shock perceptible by the patient.
 8. The method of claim1, wherein generating one of at least two distinct signals, each saidsignal indicative of a different therapeutic treatment, comprisesgenerating one of at least four distinct signals.
 9. The method of claim1, wherein generating one of at least two distinct signals, each saidsignal indicative of a different therapeutic treatment, comprisestransmitting at least one message through the patient's skin to a remotedevice.
 10. The method of claim 9, further comprising providing writtenor visual instructions to the patient.
 11. The method of claim 9,wherein said remote device is a hand held device.
 12. The method ofclaim 9, wherein said remote device is a tabletop display.
 13. Themethod of claim 1, wherein generating one of at least two distinctsignals, each said signal indicative of a different therapeutictreatment, comprises transmitting at least one message through thepatient's skin to a device for generating spoken instructions to thepatient.
 14. The method of claim 13, wherein said spoken instructions tothe patient comprise instructions regarding a responsive action to beperformed by the patient.
 15. The method of claim 13, wherein saidspoken instructions to the patient comprise therapeutic instructions.16. The method of claim 15, wherein said therapeutic instructionscomprise instructions regarding the patient's medication.
 17. The methodof claim 13, wherein to spoken instructions comprise synthesized speech.18. The method of claim 13, wherein the spoken instructions comprise arecorded voice.
 19. The method of claim 18, wherein said recorded voicecomprises the actual recorded voice of the patient's physician.
 20. Themethod of claim 1, wherein the step of implanting a cardiac pacing leadcombined with a pressure transducer substantially permanently within themedical patient further comprises implanting said cardiac pacing leadcombined with a pressure transducer substantially permanently within themedical patient in a location selected from the group consisting of: theleft atrium, a pulmonary vein, the left atrial appendage and the septalwall.
 21. The method of claim 1, wherein implanting the cardiac pacinglead combined with the pressure transducer within the medical patientcomprises: approaching the left atrium through the right atrium;penetrating the patient's atrial septum; and positioning the pressuretransducer inside the patient's left atrium.
 22. The method of claim 21,and further comprising approaching the right atrium through the superiorvena cava.
 23. The method of claim 21, and further comprisingapproaching the right atrium through the inferior vena can.
 24. Themethod of claim 1, wherein implanting the cardiac pacing lead combinedwith the pressure transducer substantially permanently within themedical patient comprises advancing the cardiac pacing lead partiallyinto a pulmonary vein connected to the left atrium while positioning thepressure transducer within the left atrium.
 25. The method of claim 1,wherein implanting the pressure transducer substantially permanentlywithin the medical patient comprises: advancing a first lead componentcarrying anchoring apparatus to the left atrium and deploying theanchoring apparatus to anchor the first lead component to the patient'satrial septum; and advancing a cardiac pacing lead combined with apressure transducer along the first lead component until the cardiacpacing lead is in a position wherein the pressure transducer ispositioned within the patient's loft atrium.
 26. The method of claim 1,wherein communicating the signal indicative of the appropriatetherapeutic treatment comprises operating a mechanical vibrator toproduce a vibration perceptible by the patient.
 27. The method of claim1, wherein communicating the signal indicative of the appropriatetherapeutic treatment comprises operating a transmitter to sendinformation to a remote receiver.
 28. The method of claim 1, furthercomprising operating power management circuitry to deny power to atleast some portions of the signal processing apparatus during periods ofrelative inactivity between periods of active operation of thoseportions of the signal processing apparatus.
 29. The method of claim 1,wherein operating the signal processing apparatus to generate saidinstructive signal indicative of an appropriate therapeutic treatmentcomprises computing mean left atrial pressures based on multipleindividual signals generated by the pressure transducer.
 30. The methodof claim 1, wherein operating the signal processing apparatus togenerate said instructive signal indicative of an appropriatetherapeutic treatment comprises generating an instructive signalindicative of an appropriate therapeutic treatment comprising areduction in the normal dose of at least one medication taken by thepatient.
 31. The method of claim 1, wherein communicating the signalindicative of the appropriate therapeutic treatment to the patientcomprises communicating to the patient at least one predeterminedsequence comprising multiple individual signal pulses perceptible by thepatient.
 32. The method of claim 1, wherein operating the signalprocessing apparatus to generate an instructive signal indicative of anappropriate therapeutic treatment comprises diagnosing a cause ofworsening CHF.
 33. A method for treating congestive heart failure in amedical patient, the method comprising: implanting a flexible sensorlead coupled to a pressure transducer substantially permanently withinthe medical patient; implanting a cardiac pacing lead to runsubstantially parallel to said flexible lead; operating the pressuretransducer to generate a signal indicative of fluid pressure within theleft atrium; communicating the signal indicative of the fluid pressurewithin the left atrium to signal processing apparatus; operating thesignal processing apparatus to generate an instructive signal indicativeof an appropriate therapeutic treatment, wherein operating the signalprocessing apparatus comprises generating one of at bait two distinctsignals, each said signal indicative of a different therapeutictreatment; and communicating the instructive signal indicative of theappropriate therapeutic treatment to the patient.
 34. The method ofclaim 33, wherein at least one of the pressure transducer or the signalprocessing apparatus is at least partially contained within a housing,wherein the housing is permanently implanted within the patient's body.35. The method of claim 33, wherein the step of implanting a flexiblelead coupled to a pressure transducer substantially permanently withinthe medical patient further comprises implanting said flexible leadsubstantially permanently in a location selected from the groupconsisting of: the left atrium, a pulmonary vein, the left atrialappendage, and the atrial septal wall.
 36. A method for treatingcongestive heart failure in a medical patient, the method comprising:implanting a defibrillator lead combined with a sensor lead connected toa pressure transducer substantially permanently within the medicalpatient; operating the pressure transducer to generate a signalindicative of fluid pressure within the left atrium; communicating thesignal indicative of the fluid pressure within the left atrium to signalprocessing apparatus; operating the signal processing apparatus togenerate an instructive signal indicative of an appropriate therapeutictreatment, wherein operating the signal processing apparatus comprisesgenerating one of at least two distinct signals, each said signalindicative of a different therapeutic treatment; and communicating theinstructive signal indicative of the appropriate therapeutic treatmentto the patient.
 37. The method of claim 36, wherein at least one of thedefibrillator lead, the pressure transducer or the signal processingapparatus is at least partially contained within the housing.
 38. Themethod of claim 36, wherein the step of implanting a defibrillator leadcombined with a pressure transducer substantially permanently within themedical patient further comprises implanting said defibrillator leadcombined with a pressure transducer substantially permanently in alocation selected front the group consisting of: the left atrium, apulmonary vein, the left atrial appendage and the septal wall.
 39. Amethod for treating congestive heart failure in a medical patient, themethod comprising: implanting a flexible lead coupled to a pressuretransducer substantially permanently within the medical patient;implanting a defibrillator lead to run substantially parallel to saidflexible lead; operating the pressure transducer to generate a signalindicative of fluid pressure within the left atrium; communicating thesignal indicative of the fluid pressure within the left atrium to signalprocessing apparatus; operating the signal processing apparatus togenerate an instructive signal indicative of an appropriate therapeutictreatment, wherein operating the signal processing apparatus comprisesgenerating one of at least two distinct signals, each said signalindicative of a different therapeutic treatment; and communicating toinstructive signal indicative of the appropriate therapeutic treatmentto the patient.
 40. The method of claim 39, wherein at least one of thedefibrillator lead, the pressure transducer or the signal processingapparatus is at least partially contained within a housing, wherein thehousing permanently implanted within the patient's body.
 41. The methodof claim 39, wherein the step of implanting a flexible lead coupled to apressure transducer substantially permanently within the medical patientfurther comprises implanting said flexible lead coupled to a pressuretransducer substantially permanently in a location selected from togroup consisting of: the left atrium, a pulmonary vein, the left atrialappendage and the septal wall.